(Reuters) - Black workers in the United States have dropped further behind white people in wages over the past four decades, largely because of racial discrimination in the labor market, according to a study released on Tuesday.

The growing wage gap represents a stubborn disparity that researchers with the Washington-based Economic Policy Institute said should receive closer attention from government officials.

The study by the think tank compared the 2015 wages of African-American and white workers with 1979 pay levels, when, according to other research, income for all but the highest-earning workers began growing at a slower rate than productivity.

In 2015, black men's average hourly wages were 31 percent lower than for white men, compared with a 22 percent discrepancy in 1979, according to the report.

The study said black women were nearly on par with white women in wages in 1979. By 2015, the economic divide had widened to 19 percent.

In line with other research on the gender wage gap, the authors said black women were even further behind white men in earnings than they were four decades ago.

"It's just another way to sort of draw our attention that we don't live in a post-racial America," Valerie Rawlston Wilson, an author of the report, said in a phone interview on the findings.

During the late 1990s, the gap narrowed because of tighter labor markets and hikes in the U.S. minimum wage.

Since then, it has expanded.

The Economic Policy Institute report found the wage gap persisted even when controlling for differences between black and white workers in educational attainment, experience or geographic locale.

"We find that discrimination is probably the largest single factor driving the change in the gap," Wilson said.

Even so, the report found factors such as education and experience levels explained more than a quarter of the black-white wage gap for men and over a third of the disparity for women.

The low representation of African-Americans in executive ranks has also played a significant role, according to the report, which said much of the total growth in incomes over the past four decades had gone to chief executives and other high-level managers. Only 3 percent of U.S. chief executives are African-American.

The authors of the report recommended that U.S. government officials more consistently enforce anti-discrimination laws in the labor market.